Voltage Rail Monitoring to Detect Electromigration

ABSTRACT

A method detects electromigration in a field replaceable unit. An integrated circuit, which is within a field replaceable unit (FRU) in an electronic device, is quiescented. An isolation power switch applies a test voltage from a field power source to a target voltage rail in the integrated circuit. An isolation power switch isolates the target voltage rail from the field power source. A voltage sensor coupled to the target voltage rail measures a field voltage decay rate for the target voltage rail. A voltage record comparator logic within the integrated circuit compares the field voltage decay rate to an initial voltage decay rate for the target voltage rail. In response to a difference between the field voltage decay rate and the initial voltage decay rate for the target voltage rail exceeding a predetermined limit, a signal is sent to an output device.

BACKGROUND

The present disclosure relates to the field of electronic circuits, andspecifically to electronic circuits that are vulnerable toelectromigration.

Electromigration is the movement of conductive materials caused by atransfer of momentum between electrons and ions in the conductivematerial. The displaced conductive material can cause one or moreconductive tendrils to form. Given a first conductor in close proximityto a second conductor, over time a conductive tendril may form betweenthe first and second conductor.

SUMMARY

A method detects electromigration in a field replaceable unit (FRU). Anintegrated circuit, which is within a FRU in an electronic device, isquiescented. An isolation power switch applies a test voltage from afield power source to a target voltage rail in the integrated circuit,where the test voltage is below an operational voltage for transistorswithin the integrated circuit. An isolation power switch isolates thetarget voltage rail from the field power source. A voltage sensorcoupled to the target voltage rail measures a field voltage decay ratefor the target voltage rail wherein the voltage sensor couples thetarget voltage rail to a reference voltage source. A voltage recordcomparator logic within the integrated circuit compares the fieldvoltage decay rate to an initial voltage decay rate for the targetvoltage rail. In response to a difference between the field voltagedecay rate and the initial voltage decay rate for the target voltagerail exceeding a predetermined limit, a signal is sent to an outputdevice coupled to the voltage record comparator logic, where the outputdevice indicates that a difference between the initial voltage decayrate and the field voltage decay rate for the target voltage railexceeds a predefined limit, and where the difference between the initialvoltage decay rate and the field voltage decay rate for the targetvoltage rail is a result of current leakage caused by electromigrationin the integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary system and network in which the presentdisclosure may be implemented;

FIG. 2 illustrates an exemplary integrated circuit in a fieldreplaceable unit (FRU) in accordance with one or more embodiments of thepresent invention;

FIG. 3 depicts exemplary charging and discharging rate curves for atarget voltage rail with and without defects in the integrated circuitshown in FIG. 2;

FIG. 4 illustrates an exemplary voltage monitor as used in accordancewith one or more embodiments of the present invention to monitor voltagedecay in the target voltage rail depicted in FIG. 2;

FIG. 5 is a high level flow chart of one or more steps performed by oneor more processors and/or other hardware devices to test and respond toa field replaceable unit exhibiting electromigration in accordance witha first embodiment of the present invention; and

FIG. 6 is a high level flow chart of one or more steps performed by oneor more processors and/or other hardware devices to test and respond toa field replaceable unit exhibiting electromigration in accordance witha second embodiment of the present invention.

DETAILED DESCRIPTION

The present invention may be utilize a system, a method, and/or acomputer program product. The computer program product may include acomputer readable storage medium (or media) having computer readableprogram instructions thereon for causing a processor to carry outaspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Electromigration (EM) is the redistribution of material over time incurrent carrying paths (chip traces, ball grid arrays, laminate traces,etc.) common to the semiconductor industry. This is a slow process thatcan cause functional failure due to voids (where material was removed)or shorts (where material was deposited).

Previously, detection of resistive growths has relied on the occurrenceof failures. The present invention, however, monitors growing tendrilsaffecting voltage rails before a fatal short develops. That is, thepresent invention identifies defects which exist at Time Zero (T0) thatare not severe enough to (a) cause a functional impact or (b) even bedetected by prior art test methods.

Thus, the present invention provides a mechanism to detect EM inducedgrowing resistive shorts affecting voltage rails over time in the fieldbefore they cause a functional failure for a customer/user.

The present invention is capable of detecting other types oftime-dependent defect leakage mechanisms beyond EMs, should they occur.That is, the present invention can be used to detect any type of defectin a circuit, assuming that such defects result in an anomalous voltagedecay in an isolated voltage rail in the circuit.

In one or more embodiments, firmware integration enables the system tocontrol workloads to a chip under test with minimal system impact byproviding a mechanism to measure the voltage discharge rate (voltagesense) as a detector of resistive shorts affecting voltage rails andother structures. This allows the system to compare measurements to timezero readings in order to determine effects over time.

With reference now to the figures, and in particular to FIG. 1, there isdepicted a block diagram of an exemplary system and network that may beutilized by and/or in the implementation of the present invention. Someor all of the exemplary architecture, including both depicted hardwareand software, shown for and within computer 101 may be utilized bysoftware deploying server 149 and/or the device under test (DUT) 151(e.g., the field replaceable unit (FRU) 204) shown in FIG. 1).

Exemplary computer 101 includes a processor 103 that is coupled to asystem bus 105. Processor 103 may utilize one or more processors, eachof which has one or more processor cores. A video adapter 107, whichdrives/supports a display 109, is also coupled to system bus 105. Systembus 105 is coupled via a bus bridge 111 to an input/output (I/O) bus113. An I/O interface 115 is coupled to I/O bus 113. I/O interface 115affords communication with various I/O devices, including a keyboard117, a mouse 119, a media tray 121 (which may include storage devicessuch as CD-ROM drives, multi-media interfaces, etc.), and external USBport(s) 125. While the format of the ports connected to I/O interface115 may be any known to those skilled in the art of computerarchitecture, in one embodiment some or all of these ports are universalserial bus (USB) ports.

As depicted, computer 101 is able to communicate with a softwaredeploying server 149 and/or the DUT 151 using a network interface 129.Network interface 129 is a hardware network interface, such as a networkinterface card (NIC), etc. Network 127 may be an external network suchas the Internet, or an internal network such as an Ethernet or a virtualprivate network (VPN). In one or more embodiments, network 127 is awireless network, such as a Wi-Fi network, a cellular network, adedicated radio-frequency (RF) network, a near-field communication (NFC)channel, etc.

A hard drive interface 131 is also coupled to system bus 105. Hard driveinterface 131 interfaces with a hard drive 133. In one embodiment, harddrive 133 populates a system memory 135, which is also coupled to systembus 105. System memory is defined as a lowest level of volatile memoryin computer 101. This volatile memory includes additional higher levelsof volatile memory (not shown), including, but not limited to, cachememory, registers and buffers. Data that populates system memory 135includes computer 101's operating system (OS) 137 and applicationprograms 143.

OS 137 includes a shell 139, for providing transparent user access toresources such as application programs 143. Generally, shell 139 is aprogram that provides an interpreter and an interface between the userand the operating system. More specifically, shell 139 executes commandsthat are entered into a command line user interface or from a file.Thus, shell 139, also called a command processor, is generally thehighest level of the operating system software hierarchy and serves as acommand interpreter. The shell provides a system prompt, interpretscommands entered by keyboard, mouse, or other user input media, andsends the interpreted command(s) to the appropriate lower levels of theoperating system (e.g., a kernel 141) for processing. While shell 139 isa text-based, line-oriented user interface, the present invention willequally well support other user interface modes, such as graphical,voice, gestural, etc.

As depicted, OS 137 also includes kernel 141, which includes lowerlevels of functionality for OS 137, including providing essentialservices required by other parts of OS 137 and application programs 143,including memory management, process and task management, diskmanagement, and mouse and keyboard management.

Application programs 143 include a renderer, shown in exemplary manneras a browser 145. Browser 145 includes program modules and instructionsenabling a world wide web (WWW) client (i.e., computer 101) to send andreceive network messages to the Internet using hypertext transferprotocol (HTTP) messaging, thus enabling communication with softwaredeploying server 149 and other systems.

Application programs 143 in computer 101's system memory (as well assoftware deploying server 149's system memory) also include anElectromigration Detection Logic (EDL) 147. EDL 147 includes code forimplementing the processes described below, including those described inFIGS. 2-6. In one embodiment, computer 101 is able to download EDL 147from software deploying server 149, including in an on-demand basis,wherein the code in EDL 147 is not downloaded until needed forexecution. In one embodiment of the present invention, softwaredeploying server 149 performs all of the functions associated with thepresent invention (including execution of EDL 147), thus freeingcomputer 101 from having to use its own internal computing resources toexecute EDL 147.

The hardware elements depicted in computer 101 are not intended to beexhaustive, but rather are representative to highlight essentialcomponents required by the present invention. For instance, computer 101may include alternate memory storage devices such as magnetic cassettes,digital versatile disks (DVDs), Bernoulli cartridges, and the like.These and other variations are intended to be within the spirit andscope of the present invention.

With reference now to FIG. 2, an exemplary integrated circuit (IC) 202within a field replaceable unit (FRU) 204 is presented in accordancewith one or more embodiments of the present invention. As suggested bythe name, FRU 204 is a circuit board that is easily replaceable in thefield using few if any tools. FRU 204 may be part of a computer systemor any other electronic device, such as a controller for manufacturingequipment, etc.

As shown in FIG. 2, IC 202 has an isolation power switch 206, whichelectrically couples a power source 208 to a target voltage rail 210.Target voltage rail 210 provides electrical voltage to one or morecircuit node(s) 212, such as execution units, memory devices,controllers, etc.

Within IC 202 is a voltage sensor 214, which measures the amount ofvoltage on the target voltage rail 210 as compared to a referencevoltage source 215. In various embodiments of the present invention, thereference voltage source 215 is a ground, a negatively biased voltagesource (e.g., another voltage rail, not shown, that increases a voltagepotential of the target voltage rail 210), or a positively biasedvoltage source (e.g., another voltage rail, not shown, that reduces thevoltage potential of the target voltage rail 210). Thus, a negativelybiased voltage source will induce voltage decay in the target voltagerail 210 when isolated from power source 208 and while circuit node(s)212 are quiesced, and a positively biased voltage source will impedevoltage decay in the target voltage rail 210 when isolated from powersource 208 and while circuit node(s) 212 are quiesced.

A memory supervisor 216 takes periodic (e.g., under the control of aclock 218) voltage measurements from the voltage sensor 214 and storesthem in a voltage memory 220. These voltage measurements are taken 1) atthe time the IC 202 is manufactured and/or installed on the FRU 204 aswell as 2) while the IC 202/FRU 204 are in the field (i.e., are part ofan operational system).

That is, when the IC 202 was manufactured, a baseline for voltage decayof the target voltage rail 210 when isolated from a power source ismeasured by the voltage sensor 214. As shown in exemplary purposes, thisvoltage has a linear decay of 0.1 V_(Dc) every time unit. For example,as shown in FIG. 2 assume that when the IC 202 was manufactured, thetarget voltage rail 210 was 1) connected by isolation power switch 206(i.e., isolation power switch 206 is closed) to a power source (notshown) at the manufacturer's facility, which put 5 V_(DC) onto thetarget voltage rail 210, and 2) was then isolated from that power sourceby isolation power switch 206 (i.e., isolation power switch 206 isopened). The voltage decay on the target voltage rail 210 at the time ofmanufacture thus went from 5.0 V_(DC) at time T0, down to 4.9 V_(DC) attime T1, down to 4.8 V_(DC) at time T2, and then down to 4.7 V_(DC) attime T3, as shown in the column for the reference voltage readingsV_(ref). Assume further that this voltage decay is normal for IC 202.

Assume now that, while in the field (i.e., in the environment of asystem in which the FRU 204 is installed), that the target voltage rail210 was 1) connected by isolation power switch 206 (i.e., isolationpower switch 206 is closed) to a field power source 208 while installedin the computer system, which also put 5 V_(DC) onto the target voltagerail 210, and 2) was then isolated from that power source by isolationpower switch 206 (i.e., isolation power switch 206 is opened). Thevoltage decay on the target voltage rail 210 while the FRU is installedin the computer system thus went from 5.0 V_(DC) at time T0, down to 4.8V_(DC) at time T1, down to 4.6 V_(DC) at time T2, and then down to 4.4V_(DC) at time T3, as shown in the column for the present field testvoltage readings V_(tst).

As shown in graph 301 in FIG. 3, this difference in voltage decay has aspecific shape based on electromigration. That is, in both themanufacturing facility that built the IC 202 and in the field, thetarget voltage rail 210 has 5.0 V_(DC) applied by a power source (step1). In both the manufacturing facility that built the IC 202 and in thefield, the target voltage rail 210 is isolated from the power source(step 2). The voltage on the target voltage rail 210 then decays (step3).

As shown in graph 301, the voltage decay of the target voltage rail 210when the IC 202 was manufactured has a normal (e.g., linear) decay rate,as depicted by line 303. However, in the field, the voltage decay of thetarget voltage rail 210 is much more pronounced, as depicted by line305, thus taking the IC 202 into a “danger zone” 307. That is, thedanger zone is indicative of electromigration causing conductivetendrils of metal to leak voltage/current, as determined by modeling,prior tests, etc. In this example the conductive tendril causes thedecay rate to increase. However if the tendril had contacted a voltagethat was higher than the target voltage rail 210, the decay rate coulddecrease, which is also indicative of an increasingly conductive leakagepath.

Returning to FIG. 2, a voltage record comparator logic 222 compares thevalues in voltage memory 220 for V_(ref) to V_(tst). If the value(s)differences exceed a predefined value (e.g., a difference betweenV_(ref) to V_(tst) of more than 0.1 V_(DC) at one or more time periodsafter time T0), then an alarm indicator 224 (e.g., a register bit whichfirmware polls, a LED or some other early warning mechanism) will beactivated. Alternatively, a test computer (e.g., computer 101 shown inFIG. 1) can plug into input/output (I/O) 226 and retrieve readingsdirectly (or indirectly via voltage record comparator logic 222) fromvoltage memory 220.

Note that voltage record comparator logic 222 and voltage sensor 214 arecircuits that preferably are part of IC 202. Thus, in a preferredembodiment voltage record comparator logic 222 and voltage sensor 214utilize minimum components that are able to be formed on IC 202 usingphoto etching, conductor spattering, etc.

For example, consider exemplary voltage sensor 214 shown in FIG. 4. Inthis example, voltage sensor 214 has several transistors, depicted asfield effect transistors (FETs) 402 a-402 d, each of which have avoltage bias for a different voltage level before they are turned on.That is, assume that a reference resistance R_(ref) 410, which may be adelimiting resistor connected to target voltage rail 210 or may betarget voltage rail 210 itself, is being monitored by voltage sensor214. Assume further that, due to voltage biasing, FET 402 a turns onwhen exposed to 5.0 V_(DC), and that FET 402 b turns on when exposed to4.8 V_(DC), and that FET 402 c turns on when exposed to 4.6 V_(DC), andthat FET 402 b turns on when exposed to 4.4 V_(DC). The voltage memory220, using dedicated ports and/or other circuitry, loads these voltagevalues into the memory array 404, as shown in FIG. 4. That is, when eachcell in the memory array 404 is turned on by one of the FETs 402 a-402d, a preset value is loaded onto that cell.

Similarly, voltage record comparator logic 222 may be implemented as acircuit etched/plated on IC 202. For example, voltage record comparatorlogic 222 may be implemented as transistors that are arranged to turnoff and on depending on the differences in values in voltage memory 220.For example, if the V_(ref) at T2 is 4.8 V_(DC) and the V_(tst) at T2 is4.6 V_(DC), XOR chips (e.g., part of voltage record comparator logic222) can output a signal indicating that the one or more bits in thebyte that describes two values are different, thus indicating tendrilcurrent leakage caused by electromigration.

Thus, the present invention does not require probes or other testingdevices such as that used in an Iddq test or similar system, but ratheruses just a few electronic components that preferably are part of the IC202 itself.

As just mentioned, in one embodiment, the voltage sensor 214 and/orvoltage record comparator logic 222 are preferably part of IC 202.Similarly and in another embodiment, the isolation power switch 206,memory supervisor 216, clock 218, voltage memory 220, alarm indicator224, and/or I/O 226 are part of the integrated circuit 202 as depictedin FIG. 2. In an alternative embodiment, one or more of the isolationpower switch 206, memory supervisor 216, clock 218, voltage memory 220,voltage record comparator logic 222, alarm indicator 224, and/or I/O 226are mounted on a circuit board (not depicted), which is part of the FRU204. However, in one embodiment, target voltage rail 210 and circuitnode(s) 212 are only part of IC 202.

Thus, in an embodiment of the present invention depicted in FIG. 2, anIC 202, which may incorporated into an FRU 204, is presented. The targetvoltage rail 210 provides power to at least one circuit node from thecircuit node(s) 212 in the IC 202. The isolation power switch 206selectively connects the target voltage rail 210 to a power source 208,which may be a manufacturer's power source or a field power source, asdescribed above.

A voltage sensor 214 couples the target voltage rail 210 to a referencevoltage source 215, which may be ground or a biased source (e.g., abiased other voltage rail, either on the IC 202 or on the FRU 204). Amemory supervisor 216, which is coupled to the voltage sensor 214, iscoupled to a voltage memory 220, which stores a record of an initialvoltage decay rate (V_(ref)) for the target voltage rail 210 whileisolated from a manufacturer's power source (e.g., a first embodiment ofpower source 208) and while circuits (e.g., circuit node(s) 212) on theIC 202 are quiesced. A clock 218, which is coupled to the memorysupervisor 216, triggers the memory supervisor 216 to take serialvoltage readings from the voltage sensor 214 while the target voltagerail 210 is isolated from a field power source (e.g., power source 208)to create a field voltage decay rate for the target voltage rail 210.

A voltage record comparator logic 222 compares the initial voltage decayrate to the field voltage decay rate for the target voltage rail 210.The voltage record comparator logic 222 may be implemented in softwareand/or firmware using processing components (not depicted) on IC 202, orvoltage record comparator logic 222 may be hardware as described above.

An output device (alarm indicator 224 and/or I/O 226), which is coupledto the voltage record comparator logic 222, describes a differencebetween the initial voltage decay rate and the field voltage decay ratefor the target voltage rail that exceeds a predefined limit. Asdescribed herein, the difference between the initial voltage decay rateand the field voltage decay rate for the target voltage rail is a resultof current leakage in the integrated circuit. In a preferred embodiment,the level and/or specific pattern of difference is predetermined (basedon previous tests) to indicate that the current leakage is caused by thepresence of electromigration on the IC 202.

With reference now to FIG. 5, a high level flow chart of one or moresteps performed by one or more processors and/or other hardware devicesto test and respond to a field replaceable unit exhibitingelectromigration in accordance with a first embodiment of the presentinvention is presented. As shown in block 501, the IC 202 to be testedfor electromigration-based leakage, is quieted/quiesced (e.g., circuitnode(s) 212 are allowed to “settle down”, such that no transistors areactive, no power is being drawn, etc.)

As shown in block 503, a target voltage (e.g., 5.0 V_(DC)) is applied tothe target voltage rail 210 at a voltage (i.e., V_(tar)) that will notexcite the nodes in the IC 202 (i.e., V_(tar) is less than the voltagethat will cause the circuit node(s) 212 to become active).

As shown in block 505, a determination is made as to whether or not thevoltage decay on the target voltage rail 210 is out of spec, withinspec, or within spec but nonetheless elevated. If the voltage decay iswithin spec (i.e., is close to the nominal voltage decay rate displayedby the target voltage rail 210 when it was manufactured), then theprocess ends (block 507). If the voltage decay is out of spec (i.e.,varies beyond some predefined limit from the voltage decay for targetvoltage rail 210 when it was manufactured), then a field replaceableunit call (“frucall”) is issued to replace the FRU 204. If the voltagedecay rate is elevated but still within spec, then a query is made as towhether or not the target voltage rail is on a watch list (query block511), as identified by system firmware. This watch list may be theresult of the IC 202 being tested showing elevated levels of voltagedecay in prior tests, other ICs from the same batch as IC 202demonstrating electromigration problems, IC 202 being used by missioncritical systems, etc. If IC 202 is showing a trend of worsening voltagedecay from target voltage rail 210 (query block 515), then the systemwill issue an instruction to replace the FRU 204. If this is the firsttime that the IC 202 has shown an elevated, but not out of spec, voltagedecay rate, then it is added to the watch list (block 513), andoperations resume.

With reference now to FIG. 6, a high level flow chart of one or moresteps performed by one or more processors and/or other hardware devicesto test and respond to a field replaceable unit exhibitingelectromigration in accordance with a second embodiment of the presentinvention is presented.

After initiator block 602, one or more processors quiescent anintegrated circuit that is within a field replaceable unit (FRU), wherethe FRU is a field replaceable board in an electronic device, asdescribed in block 604.

As described in block 606, one or more processors apply, via anisolation power switch, a test voltage from a field power source to atarget voltage rail in the integrated circuit, where the test voltage isbelow an operational voltage for transistors within the integratedcircuit. That is, the rail voltage (to test of electromigration leakage)being applied to target voltage rail needs to be very low - less than anFET threshold voltage, and less than a “diode drop”. FET and junctionleakages go up rapidly with voltages, making small electromigrationfaults difficult to detect. Thus, in one or more embodiments of thepresent invention, reference/test voltages being applied to targetvoltage rail 210 are between 0.3 V_(DC) and 0.2 V_(DC), which is lowerthan an FET threshold and low enough to keep junction leakages low.

As described in block 608, an isolation power switch isolates the targetvoltage rail from the field power source.

As described in block 610, a voltage sensor coupled to the targetvoltage rail measures, along with a memory supervisor and a clock, afield voltage decay rate for the target voltage rail.

As described in block 612, a voltage record comparator logic within theintegrated circuit compares the field voltage decay rate to an initialvoltage decay rate for the target voltage rail.

As described in block 614, in response to a difference between the fieldvoltage decay rate and the initial voltage decay rate for the targetvoltage rail exceeding a predetermined limit, the voltage recordcomparator logic sends a signal to an alarm on the FRU, where thedifference between the initial voltage decay rate and the field voltagedecay rate for the target voltage rail has been predetermined (e.g., byprior test results) to be a result of current leakage caused byelectromigration in the integrated circuit.

The flow chart ends at terminator block 616.

As described herein, in one embodiment of the present invention theinitial voltage decay rate was recorded upon an installation of theintegrated circuit into the field replaceable unit (FRU).

As described herein, in one embodiment of the present invention thereference voltage source is a reference voltage rail that provides abias voltage to the target voltage rail.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of various embodiments of the present invention has beenpresented for purposes of illustration and description, but is notintended to be exhaustive or limited to the present invention in theform disclosed. Many modifications and variations will be apparent tothose of ordinary skill in the art without departing from the scope andspirit of the present invention. The embodiment was chosen and describedin order to best explain the principles of the present invention and thepractical application, and to enable others of ordinary skill in the artto understand the present invention for various embodiments with variousmodifications as are suited to the particular use contemplated.

Any methods described in the present disclosure may be implementedthrough the use of a VHDL (VHSIC Hardware Description Language) programand a VHDL chip. VHDL is an exemplary design-entry language for FieldProgrammable Gate Arrays (FPGAs), Application Specific IntegratedCircuits (ASICs), and other similar electronic devices. Thus, anysoftware-implemented method described herein may be emulated by ahardware-based VHDL program, which is then applied to a VHDL chip, suchas a FPGA.

Having thus described embodiments of the present invention of thepresent application in detail and by reference to illustrativeembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of the presentinvention defined in the appended claims.

What is claimed is:
 1. A method for detecting electromigration in afield replaceable unit, the method comprising: quiescenting anintegrated circuit that is within a field replaceable unit (FRU),wherein the FRU is a field replaceable board in an electronic device;applying, via an isolation power switch, a test voltage from a fieldpower source to a target voltage rail in the integrated circuit, whereinthe test voltage is below an operational voltage for transistors withinthe integrated circuit; isolating, via the isolation power switch, thetarget voltage rail from the field power source; measuring, by a voltagesensor coupled to the target voltage rail, a field voltage decay ratefor the target voltage rail, wherein the voltage sensor couples thetarget voltage rail to a reference voltage source; comparing, via avoltage record comparator logic within the integrated circuit, the fieldvoltage decay rate to an initial voltage decay rate for the targetvoltage rail; and in response to a difference between the field voltagedecay rate and the initial voltage decay rate for the target voltagerail exceeding a predetermined limit, sending, via an output devicecoupled to the voltage record comparator logic, a signal to an alarmassociated with the FRU, wherein the difference between the initialvoltage decay rate and the field voltage decay rate for the targetvoltage rail has been predetermined to be a result of current leakage inthe integrated circuit.
 2. The method of claim 1, wherein the initialvoltage decay rate was recorded upon an installation of the integratedcircuit into the field replaceable unit (FRU).
 3. The method of claim 1,wherein the current leakage is a result of electromigration in theintegrated circuit.
 4. The method of claim 1, wherein the initialvoltage decay rate was recorded upon a final manufacturing of theintegrated circuit.
 5. The method of claim 1, wherein the initialvoltage decay rate was recorded upon a final installation of theintegrated circuit into the FRU.
 6. The method of claim 1, wherein thereference voltage source is a ground. The method of claim 1, wherein thereference voltage source is a reference voltage rail.
 8. The method ofclaim 8, wherein the reference voltage rail provides a bias voltage tothe target voltage rail.
 9. The method of claim 1, wherein the outputdevice is an input/output connector to a test device.
 10. The method ofclaim 1, wherein the output device is an alarm indicator.